Ignition and control system for fragmented wood-type fuel furnaces

A new and improved furnace system for automatically controlled continuous and efficient combustion of fragmented wood-type fuels such as chipped hogged, and pelletized wood, bark, wood waste, and logging residues, said furnace system adapted for utilizing and retrofitting conventional hot air, steam and hot water furnaces or boilers having a conventional combustion chamber, heat exchanger, and firing means, said new furnace system comprising:

• wood-type fuel combustion chamber means formed by an enclosure of refractory material and having a combustion surface for supporting fragmented wood-type fuel for efficient combustion of the wood-type fuel at elevated temperatures, said wood-type fuel combustion chamber means comprising an enclosure of refractory material forming a primary combustion section and an after burner section within said enclosure and wherein said combustion surface is mounted in the primary combustion section for receiving the fragments of wood-type fuel and for supporting the combusting fuel, said enclosure formed with an opening over the combustion surface for gravity delivery of fragmented wood-type fuel downwardly onto said surface;
• fragmented wood-type fuel feeding means for trickle feeding wood-type fuel fragments at selected uniform rates and for introducing the trickle fed fuel fragments onto the combustion surface of the wood-type fuel combustion chamber means;
• flame passageway means for coupling the wood-type fuel combustion chamber means with the combustion chamber or plenum of a conventional furnace to be retrofitted;
• electric igniter means for igniting wood-type fuel supported on the combustion surface, said electric igniter means comprising heating element means operatively formed for achieving flash point temperatures of the fuel to be ignited, shroud means enclosing said heat element means and operatively communicating at one end with the wood-type fuel combustion chamber means above said combustion surface adjacent wood-type fuel supported on said surface, said shroud means open at said end to expose wood-type fuels supported on the combustion surface to radiant heat from said heating element means for ignition by radiant heat without the heating element means contacting the wood-type fuels, and blower means coupled to the other end of said shroud means for delivering air over the heating element means thereby cooling the heating element means and delivering heated combustion air to the wood-type fuel;
• flame sensor means positioned relative to the wood-type fuel combustion chamber means for sensing the presence of flames from wood-type fuels supported in the combustion chamber, said flame sensor means comprising a first flame sensor positioned relative to the wood-type fuel combustion chamber means over the combustion surface looking downwardly for sensing the presence of flames from above said surface, and a second flame sensor positioned relative to the wood-type fuel combustion chamber means at the side and looking across the flame path for sensing the presence of flames passing from the primary combustion section to the afterburner section of the combustion chamber, said first and second sensors coupled in parallel in the control circuit means for concurrent control of the electric igniter means heating element means;
• and control circuit means for controlling and sequencing operation of the elements of the furnace system, said control circuit means operatively coupling said heating element means and flame sensor means for switching off said heating element means upon sensing flames from the wood-type fuel, said control circuit means comprising timing means for turning off the heating element means after a specified period of time if flames are not sensed by the flame sensor means.

A new and improved furnace system for providing automatic, continuous and efficient burning of chipped, hogged, pelletized, or other fragmented wood-type fuel, said furnace system comprising:

• heat exchanger means having an inlet for receiving hot combustion gases and a chimney flue outlet, said heat exchanger means constructed and arranged for transferring heat of combustion gases to a heat transfer medium;
• wood-type fuel combustion chamber means formed by an enclosure of refractory material for combustion of fragmented wood-type fuel at elevated temperatures to substantially complete combustion, said enclosure formed with a primary combustion section, and an afterburner section including flame passageway means, a combustion surface positioned in the primary combustion section for receiving the fragments of wood-type fuel and for supporting the combusting fuel, said enclosure formed with an opening above the combustion surface for gravity feed of fuel onto said surface, said enclosure formed with combustion air draft inlet in the primary combustion section in the vicinity of said surface for introducing combustion air, and a draft outlet spaced from the combustion surface in the afterburner section for venting the products of combustion to the heat exchanger means;
• electric igniter means for igniting wood-type fuel supported on the combustion surface, said electric ingiter means comprising heating element means operatively formed for achieving flash point temperatures of the fuel to be ignited, shroud means enclosing said heating element means and operatively communicating at one end with the combustion chamber means above the combustion surface and adjacent wood-type fuel supported on said surface, said shroud means opened at said end to expose wood-type fuel supported on the surface to radiant heat from the heating element means, and first blower means coupled to the other end of said shroud means for delivering air over the heating element means thereby cooling the heating element means and delivering heated combustion air to the wood-type fuel supported on said surface;
• flame sensor means positioned relative to the combustion chamber means for sensing the presence of flames from wood-type fuel supported in the combustion chamber means;
• fragmented wood-type fuel feeding means comprising conveyor means for trickle feeding fragmented wood-type fuel at selected uniform rates to a position over the wood fuel combustion chamber means and the opening over said combustion surface;
• said combustion chamber means opening for gravity feed of wood-type fuel fragments from the conveyor means to the combustion surface affording at least a first break in the fuel line thereby to prevent propagation of combustion up the fuel line from the combustion chamber means into the fragmented wood-type fuel feeding means;
• means for inducing a draft through the combustion chamber means and heat exchanger means at least during start-up of the furnace system;
• and control circuit means for controlling and sequencing the elements of said furnace system, said control means operatively coupled to turn on the wood-type fuel feeding means and first blower means and actuate the electric igniter means for igniting wood-type fuel fragments received on the combustion grate, said control means operatively coupling said flame sensor means and heating element means for switching off said heating element means upon sensing flames from the wood-type fuel.